The Design And Research Of 8 Bit Current-Mode Analog To Digital Converter

A new current mode A/D converter Analog to Digital Converter is presented in this paper, based on a Parallel (flash) and Pipelined A/D Converter. With the rapid development of computer, signal process and micro-electronic technology, new and advanced electron system comes forth largely, In the past twenty years, digital IC development improves signal process ability. This systems are be used for continuous time signal, including video, voice, medicine imaging, radar, instrument, consumed electrical appliance, and long-distance communication so on. Their successful use attribute to the rapid development of ADC (It can convert continuous signal to digital signal, which is discrete and binary system .At the same time, the output of ADC is convenient for accurate and high speed digital signal process). In a general way, according to different request of digital signal, the circuit structure, resolution, sample and conversion rate of the ADC is also different. Compared all kinds of ADC structure, advantage and disadvantage, flash and pipelined structure is used. The structure combines advantages of the two methods, which are high conversion rate and high resolution. At the same time, current mode approach is used for reducing power. So this method is advisable, considered many factors. The principle of the circuits are stated: firstly, realize 4 bit current mode flash ADC, the digital result is sent to DAC, then subtracted by input current, pass current amplifier, at last get to subsequent 4 bit flash ADC. Its result and high 4 bit digital output are whole output of 8 bit ADC. The ADC includes current mirror, current reference, current comparators, current amplifier and DAC so on. The circuits use full custom design method from basic circuit cell to circuit system. Because of use of current mode approach, the ADC circuit structure is novel and simple, without subtracter and sample-hold circuits. So the power is reduced largely. The A/D converter needs a few current reference and current comparators. The A/D circuit design uses input method of the circuit schematic diagram. Cadence CAD tools are used to simulate and verify the ADC function and performance with standard 0.6um CMOS technology of Wuxi CSMC-HJ Semiconductor Co.. Ltd. The simulated results satisfy the request of design. 8 bit current-mode ADC is realized. It has a conversion rate of 10MHz, a power dissipation of 8.67mW.